The invention describes the preparation of alkali metal aluminosilicates, in particular crystalline aluminosilicates having,the P-structure. These materials are of value as a component in detergent formulations in which they remove calcium and magnesium hardness ions by ion exchange. They also have other properties which provide additional benefits when used in detergent formulations. These aluminosilicates will be referred to as zeolite P in this description.
While the utility of zeolite P in detergent formulations has been acknowledged, for example in European Patent Application 0384070 (Unilever), they must be manufactured by a commercially effective process in order to become available on the market place. Thus, while the properties of a material may make it a useful commercial commodity, its manufacture has to be optimised for large scale production.
The zeolite P class includes a series of synthetic zeolite phases which may be in cubic configuration (also termed B or Pc) or tetragonal configuration (also termed P1) but is not limited to these forms. The structure and characteristics of the zeolite P class are given in xe2x80x9cZeolite Molecular Sievesxe2x80x9d of Donald W Breck (published 1974 and 1984 by Robert E Krieger of Fla. USA). The zeolite P class has the typical oxide formula:             M              2        n              ⁢          O      ·              Al        2              ⁢                  O        3            ·      1.80        -      5.00    ⁢          xe2x80x83        ⁢                  SiO        2            ·      5        ⁢          H      2        ⁢    O  
The present invention provides a process for preparing crystalline P-zeolites having Si:A1 ratios from 0.9 to 1.33, which are particularly effective as detergent builders, preferably ratios of 1.15:1 and below and more preferably 1.07:1 and below.
M is an n-valent cation which for this invention is an alkali-metal, that is lithium, potassium, sodium, caesium or rubidium with sodium and potassium being preferred and sodium being the cation normally used in commercial processes.
Thus sodium may be present as the major cation with another alkali metal present in a minor proportion to provide a specific benefit.
The process of the present invention allows the production of P-zeolite with the above defined ratios at economic yield. During the formation of the crystalline zeolite the reacted medium passes through a gel stage. A preferred embodiment of the invention is the production of P-zeolites at a silicon:aluminium molar ratio of 1.00xc2x10.05 from a synthesis gel with the same compositional ratio.
This feature results in the desired product and a filtrate liquor containing essentially only sodium hydroxide. This liquor can be recirculated, after optional concentration, e.g. by evaporation, to the preparation of the initial reactant solutions. Another advantage of producing P-zeolites from a synthesis gel with the same silicon:aliminium ratio is that all the sodium silicate and the sodium aluminate are used thus optimising the consumption of the starting material.
Moreover, for detergents applications there is a need for a product with high oil absorption.
It is a first object of the present invention to provide a process for the preparation of P zeolite having the oxide formula       M          2      n        ⁢      O    ·          Al      2        ⁢            O      3        ·          (              1.80        -        2.66            )        ⁢      xe2x80x83    ⁢            SiO      2        ·                  y        ⁢        H            2        ⁢  O
wherein y is the water content,
i. a sodium aluminate solution at a temperature of at least 25xc2x0 C. is mixed with a sodium silicate solution and a temperature of at least 25xc2x0 C. in an adequately vigorously stirred vessel in the presence of an effective amount of a slurry of P zeolite seed to form a gel having the composition,
Al203: (1.00-3.5)SiO2: (1.2-7.5)Na3O.
(25 to 450) (preferably 40 to 150) H2O
ii. ageing the gel at a temperature above about 25xc2x0 C. with adequate vigorous stirring to maintain solids in suspension for a period of at least about 0.1 hours, and
iii. separating the P zeolite product, washing and drying.
The product is washed in order to remove excess electrolytes such as caustic.
The sources of the seed zeolite P is not critical, although preferably it is added to the reactants as a previously prepared slurry. Alternatively a crystallised slurry from a previous reaction may be used. Additionally the ratio of the P-zeolite seed is not critical and a P-zeolite having a Si:Al ratio above 1.33 can be used.
That is to say the seed crystalline form drives the reaction to the P-form and the product ratio is attained from the gel ratio of the reactants. The processes of the invention can be operated at the scale required for commercial activities.
The ratios and concentrations of the aluminates and silicates used are not critical, but must be known to allow calculation of the gel and product compositions. The temperatures used will usually be well above the minimum temperature of 25xc2x0 C. and are preferably above about 60xc2x0 C. The gel composition will preferably contain about 40 to 150 moles of water per mole alumina.
The range of the silicon:aluminium ratio of the gel is wider than the corresponding ratio of the product since the silicon:aluminium ratio of the product is always between 2 and the corresponding ratio of the gel.
The period for ageing the gel to form the product zeolite is dependent on composition and temperature and will preferably be complete in about 10 hours, although the process will more preferably be completed within 5 hours for a commercial process.
Since it is particularly advantageous to produce P-zeolites at a silicon:aluminium molar ratio of 1.00xc2x10.05 from a synthesis gel with the same compositional ratio, it is a second object of the present invention to provide a process for the preparation of P zeolite having the oxide formula       M          2      n        ⁢      O    ·          Al      2        ⁢            O      3        ·          (              1.90        -        2.10            ⁢              xe2x80x83            )        ⁢      xe2x80x83    ⁢            SiO      2        ·                  y        ⁢        H            2        ⁢  O
wherein y is the water content, comprising the steps of:
i. a sodium aluminate solution having a temperature of at least 60xc2x0 C. is mixed with a sodium silicate solution at a temperature of at least 60xc2x0 C. in a stirred vessel in the presence of an effective amount of a slurry of P zeolite seed to form a gel having the composition,
Al2O3:(1.80-2.2)SiO2:(1.5-5)Na2O: (40 to 150) H2O
ii. ageing the gel at a temperature above about 60xc2x0 C. with stirring to maintain solids in suspension for a period of least about 0.1 hour, and
iii. separating the P zeolite product, washing and drying.
The process described is a particularly favourable route for preparing P zeolites having improved properties for use as detergent builders. These P zeolites have effective binding capacities for calcium of above 150, preferably above 160 mg/g, good rate of calcium uptake i.e. below 25 seconds, preferably below 10 secs and effective oil absorption i.e. at least 50 g/100 g zeolite and in the range to 100 g/100 g zeolite. Their d50 was in the range of about 0.85 to about 2.00 micron and was therefore particularly suitable as detergent builders.
It is therefore a third object of the present invention to provide a P zeolite having the oxide formula       M          2      n        ⁢      O    ·          Al      2        ⁢            O      3        ·          (              1.90        -        2.10            ⁢              xe2x80x83            )        ⁢      xe2x80x83    ⁢            SiO      2        ·                  y        ⁢        H            2        ⁢  O
wherein y is the water content
and having a calcium effective binding capacity of above 150 mg/g,an oil absorption of above 80 g of oil per 100 g of zeolite and a calcium uptake rate of below 10 seconds.
Standard Procedures
In the characterisation of the zeolite-P materials prepared by the present process the following methods were used.
i. Particle size: The average particle size (microns) was measured by a Malvern Mastersizer (Trade Mark) obtainable from Malvern Instruments, England and expressed as the d50, i.e. 50% by weight of the particles have a diameter smaller than the diameter quoted. The definitions d80 and d90 may also be used in association with the appropriate figure. Prior to measuring the particle size, the sample is dried as a thin layer (about 1.5 mm) at 110xc2x0 C. for two hours in a fan oven.
ii. Calcium uptake rate (CUR): The rate of removal of Ca++ ions from a wash liquor is an important characteristic of a detergency builder. The time, in seconds, is determined for a zeolite, at a concentration of 1.48 gdmxe2x88x923 and a temperature of 25xc2x0 C., to reduce the calcium ion concentration in a 0.01M sodium chloride solution from an initial value of 2xc3x9710xe2x88x923 M to 10xe2x88x925M. The zeolite was first equilibrated to constant weight over saturated sodium chloride solution and the water content measured.
iii. Calcium effective binding capacity (CEBC): The CEBC was measured in the presence of a background electrolyte to provide a realistic indicator of calcium ion uptake in a wash liquor environment. A sample of each zeolite was first equilibrated to, constant weight over saturated sodium chloride solution and the water content measured. Each equilibrated sample was dispersed in water (1cm3) in an amount corresponding to 1 g dmxe2x88x923 (dry), and the resulting dispersion (1 cm3) was injected into a stirred solution, consisting of 0.01M NaCl solution (50 cm3) and 0.05M CaCl2 (3.923 cm3), therefore producing a solution of total volume 54.923 cm3. This corresponded to a concentration of 200 mg CaO per litre, i.e. just greater than the theoretical maximum amount (197 mg) that can be taken up by a zeolite of Si:Al ratio 1.00. The change in Ca2+ ion concentration was measured by using a Ca2+ ion selective electrode, the final reading being taken after 15 minutes. The temperature was maintained at 25xc2x0 C. throughout. The Ca2+ ion concentration measured was subtracted from the initial concentration, to give the effective calcium binding capacity of the zeolite sample as mg CaO/g zeolite.
iv. Oil absorption: This was determined by the ASTM spatula rub-out method (American of Test Material Standards D281). The test is based on the principle of mixing linseed oil with the particulate zeolite by rubbing with a spatula on a smooth surface until a stiff putty like paste is formed which will not break or separate when it is cut with the spatula. The weight of oil used is then put into the equation:                               Oil          ⁢                      xe2x80x83                    ⁢          absorption          ⁢                      xe2x80x83                    ⁢                      (            OA            )                          =                              g            ⁢                          xe2x80x83                        ⁢            oil            ⁢                          xe2x80x83                        ⁢            absorbed            xc3x97            100                                              wt              .                              xe2x80x83                            ⁢              of                        ⁢                          xe2x80x83                        ⁢            zeolite            ⁢                          xe2x80x83                        ⁢                          (              gms              )                                                              =                  g          ⁢                      xe2x80x83                    ⁢                      oil            /            100                    ⁢          g          ⁢                      xe2x80x83                    ⁢          zeolite                    
In order to measure the oil absorption of the product, the washed filter cakes obtained after crystallisation were merely dried at; room temperature as a thin layer of about 2 mm until a solids content of at least 78% by weight was achieved, normally it was achieved in 2-3 days.
v. The form of the zeolite which was produced was established using standard XRD method.
Examples of processes of the invention will now be given to illustrate but not limit the invention.
Seed preparation
A Sample of zeolite P was produced using the following procedure to be used as seed in the subsequent examples.
1420 g of 2M sodium hydroxide solution and 445 g of commercial sodium aluminate solution (concentration 20% Na2O, 20% Al2O3) (Na2O/Al2O3=1.64) were placed in a 5 litre baffled flask connected to a reflux condenser.
The resultant solution was stirred and heated to 90xc2x0 C. 450 g of commercial sodium silicate solution ((SiO2 28.3%/13.8% Na2O w/w) SiO2/Na2O=2:1) was diluted with 1100 g of deionised water. The diluted. silicate solution was heated to 75xc2x0 C. and added to the stirred aluminate caustic solution over 18 minutes. The resultant reaction mixture gel was allowed to react at 90xc2x0 C. with stirring for 5 hours. The product was filtered, washed and dried.